On small Mammals from the Delta of the Parana. 95 



VI. — On small Mammals from the Delta of the Parana. 

 By Oldfield Thomas. 



(Published by permission of the Trustees of the British Museum.) 



By the kind hospitality of Cols. Kniglit and Povteous, and 

 the active lielp of their manager Mr. James Hunter, Mr. 

 Robin Kemp has been enabled to make a collection at Isla 

 Ella, in the delta of the Rio Parana, at the top of the La Plata 

 Estuary. 



So near Buenos Ayres, and in a general region that has 

 been visited by numbers of collectors, one did not expect any 

 novelties, and it has therefore been with the greatest interest 

 that I have found in this little collection no less than three 

 forms which prove to need description, one of these repre- 

 senting a new genus, while there is also a fine series of the 

 striking water-rat Sca2)teromys tomeatosas, liith'erto wanting 

 in the Museum collections. 



The islands where the specimens were obtained are remark- 

 able for the fact that they are more or less completely flooded 

 when a south-east wind banks up the waters of the La Plata 

 Estuary, and Mr. Kemp records that he has had to wade 

 through the rising waters to retrieve his traps, and that then, 

 the water having fallen and the traj)S been I'e-set, he has 

 again caught numbers of specimens. This shows, of course, 

 that all the local species have learnt to take refuge in trees, 

 unless they are themselves absolutely aquatic. That such 

 animals as Oryzomys, Oxymycterus^ Alcodon, and the new 

 genus Deltamys, all normally terrestrial, should thus have 

 become arboreal on occasion, is a remarkable case of adapta- 

 tion tO' local conditions. 



Neither the burrowing tuco-tuco {Ctenomys) nor the 

 common "laucha'' [Hesperomys) are contained in the collec- 

 tion, and they have no doubt been unable to live in so 

 water- logged a region. 



The collection consists of forty-eiglit specimens, and would 

 have been more had not one of Mr. Kemp^s cases fallen a 

 victim to barbarian methods of warfare, and been sunk in 

 the R.M.S. 'Drina.' Happily the lost box does not appear 

 to have contained any species unrepresented in that which 

 safely arrived. 



In this connection I should like to express the obligation 

 that the National Museum is under to the authorities of the 



